I have a small, ultra white matte 13x10 room that I need to photograph and film people in. The most important thing to me is a person's skin color. Something like this.

Yesterday I purchased some clamp work lights and a few 6500k CFL bulbs. However, after taking some test photos with these lights I noticed that the skin color of my subjects looked very white (and even green where veins where). It seems that this lighting is a bit much for people.

What is the correct temperature for shooting people in an indoor room? I also have some nasty, yellow soft-white (2300k?) and halogen lights.

4 Answers
4

The problem with fluorescent lighting isn't the color temperature, exactly. You can generally adjust white balance to account for that. If there's a green tint, that can usually be compensated for with manual white balance. But the poor color rendering is harder.

The problem is that by their nature fluorescent tubes only produce light in narrow ranges of wavelengths (depending on the composition of the gasses and phosphors used). Since colors in objects are in a sense only actually there if the matching wavelength of light can be reflected back into your eyes or camera, this means fluorescent lighting flattens color in weird ways.

This is one of those cases where the human vision system's magical qualities run us into trouble. Your brain adjusts for this so quickly that you don't really notice unless you've got a reference light source to compare to. (There's a cool little exhibit on this at the Museum of Science in Boston, if you're ever in my area.)

"Full spectrum" bulbs use a combination of gasses to cover more spectrum. But even then, it tends to be spiky and weird, not the wide incandescence of, say, the sun (or a traditional light bulb). Many fluorescent bulbs list something called CRI, or "Color Rendering Index". This isn't perfect — I don't think it's regulated, and it appears to be determined by each manufacturer, not independently. And the process / standard could stand to be updated to an approach using more rigorous scientific understanding. But, it's what we've got.

So, you want to look for bulbs advertising a CRI at least in the high 80s — 100 is perfect on the scale. There's lots more detail in the Wikipedia article on CRI.

Of course, you could avoid the problem by using incandescent (including halogen) light sources.

Of what you have in stock, the halogens will give the best image results. They'll also be very hot if you use enough of them to avoid cranking up the video gain and reducing the video quality (assuming you aren't running some really top-level pro gear). Since this question applies as much to photography as video, I'll make this a one-size-fits-all answer.

Continuous lighting is necessary for video, and has its advantages for still photography. Incandescent light sources are full-spectrum lights, but because they are "pure" black body radiators (for the most part -- there are a couple of weird exotics used in industrial applications that don't follow the rules) they can only emit "whiter" light (light with more amplitude in the blue/violet range) by running much hotter than normal. Photofloods and halogens are good examples; they run in the mid-3000K range (3200-3400), but even a modest light output comes with a huge heat penalty.

That's why LED and fluorescent solutions for continuous lighting make so much sense -- they emit light on a different principle that doesn't rely on things getting super-hot. LEDs are very efficient, but panels that are bright enough and cover enough of the visible spectrum to be useful are prohibitively expensive. Without commercial backing, LEDs are not a practical solution yet (although they may come down enough in price soon -- I remember when the brightest LEDs couldn't be seen at all under sunlight conditions, and now they're being used as traffic lights and brake lights on vehicles).

Fluorescents can be great -- but they have to be the right fluorescents. It's not the color temperature that matters (you can adjust the white balance on your camera, or select film and filter to suit), but the Color Rendering Index. Common fluorescents only use enough different phosphors (the compounds in the white powder coating the inside of the tube that convert ultraviolet to visible light) to allow you to see things, period. High-CRI bulbs (CFLs with a CRI of 90 or better) use a lot of different compounds to fluoresce across almost the entire visible spectrum. (And, as a bonus, they also use high-frequency ballasts and long-decay phosphors to eliminate flicker.)

Many of the usable CFL bulbs are sold specifically as photographic or design professional equipment, and carry (sorry) prices appropriate to that realm. But, really, forty bucks a bulb for 65-Watters isn't that bad over the long term. And there are lower-power bulbs you can buy elsewhere (like at Lowe's) -- the 25W OttLite CFLs are a particular favorite of mine for tabletop lighting. (Oddly, Ott has probably the best spectrum I've come across, but they don't actually state the CRI anywhere on their packaging or ads.)

The 25-cent (or less) Diffraction Spectrograph Solution

A quick test -- grab a CD or DVD, and look at it under the lights you want to use. Make sure that you're using a bare bulb, or for large lights, that you're far enough away from the light to make it a small source. Tilt the disc so that you get that "rainbow" going from center to edge. Who needs thousands of dollars worth of lab equipment when you can do the essentials with a scratched-up old CD? Even if you have to waste a brand-new DVD+R, you're only out a quarter.

If you can see the entire rainbow without any large gaps, you can make the light work. You may have to create a custom white balance (see your camera manual) for that particular light source, but unless your subject is a narrow-spectrum monochromatic reflector/transmitter (like if you're doing cross-polarized pictures of crystals), even a few small gaps in the spectrum won't be noticeable in the final image/video.

If you only see a few bright spots of color, nothing you can do will fix the image properly -- it may be better than total darkness, but not much. If you have a choice, use something else instead.

Keep the disc in your camera bag -- scratches won't affect its performance, and it can help you do a better job whenever you're on location.

A horrible internet connection means I didn't get to see the other great answers before posting this. If @mattdm and/or @Lyman edit the CD/DVD test into their answers, I'll withdraw this altogether. In the meantime, this answer was late to the party, and shouldn't be upvoted unless you also upvote the complete answers that were there before it.
–
user2719Mar 30 '11 at 17:55

3

Diffusion just smears the source so you see a number of overlapping rainbows, it doesn't fix the spectrum. What you'll see is a bunch of distinct colors butting into one another rather than a smooth transition between colors. I should have mentioned that it works best as a "bare bulb" test, or at least from a distance sufficient to make the light a "point source".
–
user2719Mar 30 '11 at 18:06

1

@Stan: Or perhaps you should make the CD diffraction idea more prominent in your answer, and get credit where credit is due!
–
Lyman Enders KnowlesMar 30 '11 at 19:03

2

No, it's right -- it's just that mercury vapor alone won't generate enough UV frequencies to cause all of the various phosphors used to fluoresce at a wide-enough spectrum, so additional gases are used as well as additional fluorescing compounds. Neither will come close to doing the job by itself, but there's really no point in attaching an entire physics paper to responses that are supposed to be about photography; it serves no purpose except to satisfy the curiosity of people who are more interested in gadgets than photography itself.
–
user2719Mar 30 '11 at 23:33

I've also tried using CFLs in clamp lights for photography, and I've also been disappointed with the color rendering.

Color temperature is a measurement that properly only applies to black body radiators, which produce a continuous spectrum. CFL bulbs aren't black body radiators and don't output a continuous spectrum, so the color temperatures claimed for them are largely a marketing fiction. The color temperature on the box may tell you how blue (high temperature) or how yellow (low temperature) you will perceive the bulb's light to be, overall, with your eyes, but it won't tell you very much about how colors will look in the light of the bulb. Because a CFL's spectrum isn't continuous, some colors in your scene simply aren't present in CFL light, and white balance adjustments can't ever add them back in.

A better measurement for color rendering is the Color Rendering Index, or CRI. CRIs in the 80s are good enough for general purpose illumination, and are common for CFLs. CRIs in the 90s are considered very good. Most CFL boxes don't specify a CRI, though.

Incandescent lights, including halogen lights, are very nearly ideal black body radiators, and give off a continuous spectrum. They are considered to have a perfect CRI of 100, the maximum for the scale. The light they give has a low color temperature (a yellow/orange cast) but that can be corrected in post much more convincingly than the discontinuous spectrum of fluorescent light can.

Maybe a combination of CFLs and incandescents could improve your color rendering without making too much heat. Maybe all-incandescent is the way to go. I'd say: experiment and report back.

If you're going to use fluorescent bulbs, you want a full-spectrum bulb, probably with a "CRI" rating of at least 90 or so. I've used Ott-lite for a few years, but there are now alternatives that are considerably less expensive and provide (at least very close to) the same quality. If memory serves, one I've seen used that seemed to be quite good was branded "Blue Max" (or maybe "BlueMax").